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I was sitting around today, and didn't feel like doing much so I cracked out the old 4x4 Electric shift module that had died last year on me.

So I thought I would take some pictures and explain how to re-solder damaged parts of the circuit board, or add wire to correct any broken traces.

Now a couple things I mention throughout this I will point out (for those not electrically inclined):

Traces: The little lines you see on circuit boards, these basically act as wire between components soldered to it.

Capacitors: Kind of like batteries, but store charge for a much shorter period of time. They also can not sustain very much power for a great period of time depending on the application. Appearance is often much like a pop can, or battery. It is a cylinder with two or more pins, the side with the white stripe is always negative.

Circuit Board: Contains all the traces, and electrical components of the device it is meant to be. I often refer to it as "board" in this thread. A computer motherboard is the same thing, as are many components of a computer.

IC: Integrated circuit, a tiny microchip with some kind of electrical circuit inside. Enclosed in a material that I forget.

This was out of my 94, which I replaced with the one out of a 91.. in -20c weather... anyways, I'm not entirely sure on the differences, however the older was grey, newer, black.

I started by releasing the clips near the end connectors.

Then a simple push and the other clips popped out nice and easy. Did the same for the other side as well.Note: I am lightly pushing the edge of the bottom half as well, this helps a bit.

Once the clips are released the cover easily comes of, revealing a well constructed circuit board. There is nothing holding it in, so the board will easily come out.

A quick check of the wires that come out of it, they are soldered in and don't appear to be broken or corroded. If they are they can be re-soldered in by the looks of it. It is also good to check the pins in the connector for any corrosion.

Checking the traces and pins at the bottom side of the circuit board, these show some mild to heavy corrosion.

The traces the connectors contact with look pretty bad too

In case anyone wonders were that little button goes to, here it is, a little piece of metal. When pushed it contacts a trace on the circuit board below.

Just check to make sure the IC's or little microchips all look ok (should be no burn marks, etc). There are also a couple capacitors (very top near the right) that should be checked. If the top is bulged out or if they are leaking, replace them.

These are the transistors under that heat sink, with a little bit of wiggling it pops off, there is a little metal piece in between them and the heat sync (on the label side of the chips). Applying new thermal paste might be a wise choice when re-installing the heat sink, which just clips on with that metal piece in place.

So after examining, and it appears to be salvageable, I started by sanding down the contacts for the end connectors. At this point in time I also lightly sanded between pins on the bottom of the circuit board were there is corrosion, and around that area to clean it up.An alcohol based spray can for electronics comes in handy here, or just brush off the debris and wipe it off with alcohol on a Kleenex or rag. Give it some time to dry.

Use a multimeter that can check resistance, and ensure any traces in the effected area are still in tact by using the pins on the end of the traces. Using the "beep" mode works best

Now that everything was cleaned up, I started to solder. Only apply a small amount of solder, just to cover the copper trace underneath. You can move the solder while its hot using the soldering gun/pen to push any extra near the inside of the trace (closest to circuit board). Once complete a little bit of sanding will clean it up nicely.Note: The bottom part of a dead computer power supply worked great for a stand to work on it. Also to keep the solder closer to the inside of the traces by the circuit board, you can angle the circuit board.

Here you can see the end connectors cleaned up a bit, and I had already started to re-solder some of the pins on the bottom of the board, just to ensure they were nicely connected.

Lastly finish up by soldering on any wire between pins were traces were no longer in tact (22guage or smaller stranded will be best).

The easiest way to do this? Cut your wire just a little longer then you need, and strip about 1mm or 1/16" from the end. Using the soldering gun, put a very small amount of solder on the end of the bare wire, do not let it heat up the insulation too much if avoidable. You will also notice this will shrink the insulation a little so there is more wire exposed, if there is too much just cut a bit off the wire (hence why we left extra ).

Now that you have a nice chunk of wire with solder on both ends, make sure the pins you will connect it to both have a bit of solder on them. then while heating the pin, attach the end of the wire and take the gun away once its nicely soldered to it, but don't waste too much time here or the insulation will melt. It will be somewhat tedious. Hold in place until the solder cools and is strong, repeat for the other pin you will connect it to. Lastly ensure it is not touching any bare wire to any other pin.

In my case, I ended up with thisI also added a bit of Vaseline to the pins to keep moisture out, hot glue would probably do a better job, however I didn't think about it until after. Actually it would be preferred as you can keep any wires added secured. Also, dogfriend mentions a "silicone based conformal coating" made by the same company as the contact cleaner I used, that would be much better to use, check his post for details.

Re-assembly is easy, I found it best to start with the side were the wires are coming out, and then clip it back together. You might have to fidget with it a bit to get it to nicely go back together.

And it is done.

-EDIT: This might be useful to some trying to diagnose their 4x4 problems, but I was still bored that day

Next up is to test it, which I may do later today once I am finished with the new idler pulley.

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I also added a bit of Vaseline to the pins to keep moisture out, hot glue would probably do a better job, however I didn't think about it until after. Actually it would be preferred as you can keep any wires added secured.

Actually, that same company that made the contact cleaner also makes silicone based conformal coating that you can brush on to protect against moisture. It costs about $5 for a 1 oz bottle, IIRC. We used to use it if there was any exposed copper on a board that was ok otherwise.

Thats good to know! I acquired two of those handy bottles of cleaner from a friend, but I'll keep my eye out for the other, there are a few things id like to keep protected in the truck, since mud and water here get EVERYWHERE!

EDIT: I added a note to the vaseline comment for what you just said dogfriend, referring to your post
EDIT 2: Id also like to note that the module before this would just flicker the lights randomly on the dash, and never respond to the buttons being clicked. It stranded me once before I decided to change it.

1. You can see through it even after it dries so it doesn't hide any problems.

2. It has low viscosity and high surface tension - it spreads out and covers everything with a thin coat. The liquid tape is very thick and much more difficult to spread evenly, IMO. There is also a spray version of the conformal coating.

3. They make conformal coat remover or you can use acetone to remove the conformal coating if you need to repair at some point in the future.

I'm not a conformal coat salesman or anything, its just that we used it where I used to work and it works very well. Its designed specifically for protecting PCBs.

Im not sure if you can test the voltages on it, I'm sure you could if its plugged in (which wont be easy without the case on it) but it would require some kind of reference to go by.

The only thing you can really do using the multimeter is test continuity (resistance) of the traces on the circuit board, to make sure none are broken, and if the multimeter has the ability, the resistance of the resistors, capacitance of the capacitors on it, and depending on availability of data sheets, there might be tests one could do to the IC's on the board.

hey you seem pretty good with electrical stuff i was hoping i could ask you a question! I have a 1991 explorer and ever since ive owned it i cant get it to go into 4x4 its got the push button module in it but i dont think thats whats wrong with it because the light next to my button will come on sometimes but the light on the dash never comes on any help or advice you can give me would be greatly appreciated

That was a fabulous write up. So I got bored yesterday and took mine apart. I think I have a corrosion problem. I have a fair bit of experience with rust and circuit boards, but I've never seen anything like this.